Patent Application
20130319773
In previously known forms of fluid drilling heads, it has been common to use a type of nozzle known as a “horn nozzle” having a diverging outlet portion designed to produce a powerful cavitation cloud for the cutting or breaking of rock in the drilling operation. Such a device is shown in
Further research by the applicants has shown that while the cavitation cloud generated by horn nozzles of this type is indeed powerful, it is generated at a position remote from the nozzle outlet. The zone between the cavitation cloud and the nozzle outlet is a “dead zone” which is not effective in cutting rock adjacent to the nozzle outlet. Accordingly, placement of such nozzles to generate smooth and self-advancing geometry is very difficult due to the dead zone immediately in front of the pilot jets at the leading edge of the fluid cutting head, and effective design of the fluid cutting head is also difficult due to the physical size of the horn nozzles. Prior art devices of the type shown in
The present invention therefore provides a fluid cutting head of the type having a plurality of nozzles in a rotatable nozzle assembly for cutting a bore hole in rock, said nozzles being arranged to be supplied with high pressure drilling fluid, forming jets positioned to cut adjacent rock, said nozzles including one or more generally axially facing pilot nozzles and one or more generally radially facing reaming nozzles, at least the pilot nozzles being characterised by a non-tapering outlet section such that the jet issuing therefrom is of substantially constant cross-section in a zone immediately adjacent the outlet section.
Preferably, the reaming nozzles are also characterised by a non-tapering outlet section such that the jet issuing therefrom is of substantially constantly cross-section in a zone immediately adjacent the outlet section.
Preferably, the leading part of the rotatable nozzle assembly incorporating the pilot nozzles is of significantly lesser diameter than the following part of the rotatable nozzle assembly incorporating the reaming nozzles.
Preferably, the following part of the rotatable nozzle assembly is formed in a stepwise fashion of steps of progressively increasing diameters, there being one reaming nozzle located in each step such that the jet issuing from each reaming nozzle is located close to the adjacent bore hole surface.
Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with reference to the accompanying drawings, in which:
In the preferred form of the invention, a fluid drilling head 8 typically has a rotatable nozzle assembly 9 and may incorporate other features such as a gauging ring 10 mounted at the leading end of a drill head body 11.
The more detailed configuration of the rotable nozzle assembly 9 will be described below with reference to
In the typical prior art fluid drilling heads, the rotatable nozzle assembly 13 is provided with pilot nozzles 14 and reaming nozzles 15 which are typically of a “horn nozzle” design having a diverging outlet portion. Nozzles of this type generate powerful cavitation clouds shown diagrammatically at 16 which are effective in cutting and breaking up rock. It has been found through careful laboratory testing that while the cavitation clouds 16 generated by the nozzles 14 and 15 are indeed powerful, they are remote from the nozzle outlets as clearly shown in
The present invention overcomes this deficit by providing nozzles of the type shown in
The nozzle is typically formed to sit in a counter bore 22 such that the top of the nozzle thread 23 sits flush with the base of the counter bore.
While the inlet portion 24 of each nozzle is typically tapered inwardly to increase the velocity of the high pressure water pumped through the nozzle, the outlet section 25 is formed of non-tapering section as is clearly seen in
It has been found that the use of nozzles formed to this configuration results in a jet which is effective at cutting or breaking rock immediately adjacent the outlet from the nozzle, so avoiding the dead zone 17 typically found in the prior art nozzle configurations.
In order to maximise the rock cutting effect of nozzles of this type, it has also been found most effective to form the rotatable nozzle assembly in steps such that the leading part 26 incorporating the pilot nozzles forming jet 1 and jet 2 is of significantly lesser diameter than the following part 27 of the rotatable nozzle assembly incorporating the reaming nozzles.
The reaming nozzles 3, 4, 5, and 6 are typically located to provide reaming jers as shown in
In this manner, the following part 27 of the rotatable nozzle assembly 9 is formed in a stepwise fashion of progressively increasing diameters, there being one reaming nozzle located in each step such that the jet issuing from each reaming nozzle is located close to the adjacent bore hole surface.
This has been found to be most effective in maximising the operation of each reaming jet, allowing the reaming jets to issue from their nozzles close to the surface of the bore hole to be reamed and enlarged until the final bore hole diameter is achieved. Ultimately, the bore hole diameter is controlled by the gauging ring 10.
This effect is optimised by reducing the diameter of the leading part 26 as much as physically possible so that the pilot jet rock cutting function is reduced compared with the progressive enlargement of the bore hole diameter from the reaming jets in the following stepped parts 27.
Combined with the use of nozzles of the type described above, this allows the reaming jets to operate close to the rock face and increase the diameter of the bore in a step-wise manner. There rearward facing orientation of the reaming jets also allows much more efficient rock breaking at this close proximity.
Laboratory testing has shown that the zone within about 5 mm of the outlet from each reaming jet is very destructive, and much more so than the remote cavitation cloud of the horn nozzles used in prior art devices.
The actual diameters of the nozzle outlets are selected depending on the nature of the rock to be cut, as is the pressure of the water supplied to the nozzles through the fluid drilling head. Testing has shown that drilling is effective at pressures of 48 MPa to 73 MPa. 48 MPa is better in bright coals, and 73 MPa is better in claystone bands and sandstone.
Nozzle diameters vary depending on the material and nozzle location. The front pilot nozzles need be no greater than 0.7 mm to 1.0 mm in diameter. It is best to minimise these sizes to improve net tool forward thrust, and a small change makes a big difference as they point virtually straight ahead. The reamers work well in the range between 0.5 mm and 1.3 mm, again depending on the coal conditions. The 310 m hole was drilled with 0.8 straight ahead, 0.9 forward angled, and 1.1 in the three reamers in this head. This, however, produced a penetration rate of around 1 m/min.
In this manner, a rotatable nozzle assembly for a fluid drilling head can be provided which allows faster drilling rates than has previously been achieved with prior art drilling heads and further allows more accurate control of the bore hole size, and the effective location of the reaming nozzles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011900671 | Feb 2011 | AU | national |
This invention relates to the design of the nozzles and rotatable nozzle assembly for a fluid drilling head of the type generally described in our earlier international patent application PCT/AU02/01550 (international publication No. WO 03/042491 A1), the content of which is incorporated herein by way of cross reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AU2012/000168 | 2/23/2012 | WO | 00 | 8/15/2013 |
